Jack



May 22, 1956 E. FREYSSINET JACK 2 Sheets-Sheet l Filed March l2, 1954 E SP2 I/VVFNTOR /7 fro R Mfg/5 May 22, 1956 E. FREYsslNl-:T 2,746,714

JACK

Filed March 12, 1954 2 Sheets-Sheet 2 United States Patent O Fr"ce JACK Eugne Freyssinet, Neuilly-sur-Seine, France, assigner of one-third to Ingenieurs Bureau Voor Industrie Service N. V., La Haye, Netherlands, and one-third to Tans Metaalconstructies en Zwaar Transport N. V., Rotterdam, Netherlands, both companies of Netherlands Application March 12, 1954, Serial No. 415,935

Claims priority, application France April 15, 1953 15 Claims. (Cl. 254-29) In my Patent No. 2,270,240, vI have described a method and an apparatus for tensioning and anchorage applicable to the prestressing armature-s of concrete members, the said armatures being each composed of a group of wires or cables.

In accordance with this method, the concrete member is provided, at the point at which the anchorage is to be made, with a cavity having approximately the shape of a truncated cone, bell-mouthed towards the exterior, and against the wall of which the wires of the armature, after having been tensioned to the optimum extent, are wedged by a wedge or cone forcibly introduced inside the conical layer formed by the wires. The equipment for carrying this method into effect comprises, in particular, a hydraulic jack device having two moving parts. One of these parts, provided with slots formed in its periphery, in which slots the wires are fixed in pairs by means of wedges, serves to give an initial tension to the wires, the tensioning reaction being supplied by supporting the nose of the jack on the concrete member, around the conical cavity formed in this member. The other moving part consists of an axial thrust member which, when the wires are tensioned and kept in tension by the above-mentioned rst part, enables a thrust to be applied to the anchoring wedge so as to insert it into the cavity of the member and to force the wires against the wall of this cavity, after which the jack may be put out of action and the extremities of the wires which project from the concrete member may be cut off.

The object of the present invention is to make improvements in a hydraulic jack arrangement of this kind, particularly with a view to reducing its length and, in consequence, its weight for the same power, Vto improve its efiiciency, to enable the wedges to be automatically freed and to make the application of the jack more practical and more certain.

These improvements may be effected either -separately or in combination.

In accordance with a first improvement, the body of the jack and the moving portion on which the wires to be tensioned are xed, are adapted in such a way that at the beginning of the tensioning operation, the wires secured to the jack form a conical layer larger than that of the body of the jack or of the bottom of the notches formed in this body to `house the wires, `thedilerence in conicity being such that the wires do not come in contact with the body of the jack before the tensioning operation lis completed. This overcomes the disadvantage of previous jacks in which the wires pressed against the body of the jack with increasing` force during the tensioning operation, thus giving rise to friction and losses which increased as the tension increased and ultimately assumed high values.

There is preferably provided at the front of the jack a ring in which the wires pass and the internal surface of which is given a suitable profile and forms a support for `the wires from the point at :which the Ilayer of wires has 'its greatest conicity. As lthis conicity steadily reduces 2,746,714 Patented May 22, 1956 during the operation, the friction of the wires on the internal surface also getsless and even tends towards zero if the conicity of the layer of wires at the end of the operation is the same a-s that of the member which forms an anchorage for the stretched wires in the concrete.

In accordance with another improvement, a pressure chamber arranged in the jack for the return to the position of rest of the moving portion to which the wires are attached, is combined with an arrangement of channels or of valves having automatic action provided on the jack and causing the said chamber to communicate with the cylinder of the small piston which drives in the wedge, so that the pressure inside this chamber becomes predominant when the main cylinder of the jack is placed in the exhaust position after the wires have been tightened and the wedge has been driven in. This said position may be combined with advantage with a stop member provided on the head of the jack and intended to loosen the keys or wedges which secure the wires.

Another improvement consists in the provision of a source of supply for the various chambers close to the yoke or end plug of the main cylinder and preferably parallel to the axis of that yoke and of that chamber, by means of which the supply can be centralized at one point, which is convenient for the operation of the jack. The supply of the chamber of the piston which drives-in the wedge can be effected through a hollow rod parallel to the general axis of the jack and mounted inside the main piston, in such a way that it can slide with respect to this piston.

Other improvements will be comprised in the description which follows below with regard to the attached drawings which are given ,by way of example, it being understood that the special features shown in the drawings as well as those referred to in the text, will form part of the invention.

Fig. l is a view in axial cross-section of a form of embodiment of a jack in accordance with the invention.

Fig. 2 is va transverse cross-section along the broken line II-II of Fig. l, the upper half of Fig. 2 being seen from the left in Fig. l and the lower half of Fig. 2 being -seen from the rightin Fig. 1, asindicated by the arrows at the respective ends of the section `line II-II. In Fig. 2. the broken line I-I shows the outline of the plan of Fig. 1.

Fig. 3 is an axial cross-section of another embodiment.

The `jack shown in Figs. l and 2 comprises a main cylinder l closed on one side by a screwed end-plug 2 having a fluid-tight sealing joint 2a and in which is mounted the main piston 3 provided with a Huid-tight ring 3a. This piston 3 is integral with a hollow cylindrical sleeve 4 `of large diameter which can slide in a .cylindrical portion 5 of the cylinder 1 and which is also provided with a fluid-tight ring 5a. On its outside and around the cylindrical portion 5, the cylinder 1 has a portion 6 of conical shape and of larger diameter than the remainder of the body, and in which are formed around the entire axis of the jack, wedge-shaped slots 7 which are intended to receive the wires 8 which are to be tensioned, and which are placed in pairs in these slots as well as the wedges or kkeys which serve to tix the wires rigidly in the said slots, each wedge, such as that shown at 9, being driven in between the two wires of each pair in such a way as to force .the wires between itself and the lateral walls of the slots. These lateral walls may be provided with cylindrical grooves 10 in order to facilitate the placing in position and the fixing of the wires which are to be secured to thecylinder 1 by the said wedges for the purpose of putting the wires under tension. The hollow sleeve 'lis extended towards the front of the jack by thehead 11 which is screwed at 12 on the ,said sleeve and provided with notches I3 vthrough which the wires are passed one by one. In the spaces between the notches 13 and opposite the slots 7 of the portion 6, the head 11 comprises thicker portions 14 which are intended to abut against the ends of the wedges 9 in order to provide for the automatic freeing of these wedges at the end of the tightening operation, when the cylinder 1 has sufficiently moved with respect to the piston 3 and the hollow sleeve 4, as will be explained in the later part of this description.

The length of the head 11 and the average diameter of the conical surface in which the slots 7 are formed, are such that the wires 8 to be tensioned are spaced away from the bottom of the notches 13 when the members of the jack are in the initial position shown in Figs. l to 3 and the wires are put into place in the slots 7 of the member 6, being wedged in these slots by the wedges 9. In this way, all frictiorial rubbing of the wires on the head of the jack during the tensioning operation is avoided as will also be noted from the explanation which will be given later. In order, however, to ensure satisfactory guiding of the wires in the notches 13 of the head 11, a ring-shaped member 15 is provided at the front portion of this head through which are passed and guided the wires which are retained by the internal surface 16 of this said ring, this internal surface being bell-mouthed and suitably rounded in order to provide a correct distribution of the wires between the ring and the xing slots 7. As soon as the tension is applied to the wires, the conicity of the layer of wires steadily decreases and, in consequence, the friction of the wires on the internal surface 16 of the ring 15 also decreases in relation to the tension of the wires. The losses by friction are thus less great than in the case of previously known jacks.

lt may be arranged so that the bottom of the notches 13 constitutes an extension of the generators of the conical cavity ci in such a way that all friction on the ring 15 is eliminated at the end of the tensioning operation.

A coil spring 17 of short length is provided between the screwed end plug 2 of the cylinder 1 and the piston 3.

It is housed between two cylindrical telescoping portions 1S, 19 which abut against each other at 20 at the extremity of the travel of their extension. This arrangement has for its effect, to cause the said spring 17 to return the piston 3, in the position of rest of the jack, to the position shown, at which the right-hand extremities of the wedges 9, when the latter are fully driven home, are located at a certain distance from the abutments 14 so as not to hinder the putting into place and the locking of these Wedges between the wires.

Within the interior of the hollow sleeve 4, a piston 21 is arranged to slide, the said piston having a uid-tight ring 21a and a rod 22 which passes through the head 11 and forms a projection 23 on the forward portion of the said head within the interior of the ring 15, the diameter of this extremity 23 being sufficiently small for the said extremity to be able to move in the interior of the cone formed by the wires and to come up against the wedge c which anchors the wires, in order to push in this wedge and to tighten it inside the cavity c1 of the block of concrete b, the re-inforcement of which is constituted by the Wires. A coil spring 24 which is supported between the shoulders of the rod 22, of the piston 21 and the head 11, serves to bring this piston back into the position of rest shown in Fig. l where it comes up against the circular shouldered portion 25 of the hollow rod 4. The travel of the piston 21 is,in addition, limited at its forward end 26 by the head 11.

ln the central portion of the end-plug 2 passes the rod 27, which is supported in the plug by a collar 28 and secured by an internal nut 29 screwed on to the said rod, a fluid-tight joint 27a being provided. This rod 27 slides through the piston 3, the tightness of the passage through the piston being ensured by sliding joints 30. The rod 27 is provided with two channels 31, 32. The channel 31 communicates at 33 with the chamber 34 formed in the interior of the hollow sleeve 4 of the piston 3, the

said chamber being itself in communication with the annular chamber 36 by a channel 35 of relatively small cross-section which is formed between the hollow sleeve 4 and the cylinder 1. The channel 32 has its outlet at 37 into the chamber 38 of the cylinder 1 between the endplug 2 of this cylinder and the piston 3, the telescoping members 19, 20, being naturally provided with holes or passages such as 26a in order that the fluid arriving at 37 may fill the whole chamber 38 and thus act on the entire cross-section of the piston 3. On its exterior, the rod 27 has two ilat oppositely provided faces 39, 4t), on which open the channels 31, 32 through the holes 39a, 40a. ln this way these channels can be supplied through the external flexible conduits which end in thimbles 42, 43 which are forced against the flat faces 39, 40 by screws 44, 45 which screw into lugs on the end-plug 2. The thimbles are provided with holes which are located opposite the holes 39a, 40a of the channels 31 and 32 and they are supported by the screws 44, 45 which hold them against the circular ttings 46, 47 housed inside grooves provided around the holes 39a, 40a.

The jack operates as follows:

Initially the chambers 34, 36, 38 are not under pressure, the supply'conduits which end in the thimbles 42, 43 being connected through suitable valves to the liquid reservoir. The wires to be tensioned and which are to be anchored in the ring 15 are then engaged in the notches 13 and then in the slots 7, the wires being arranged in pairs in the said slots. During this operation the jack is supported by the ring 15 against the surface of the block of concrete b around the hole in this block through which the wires extend. The wedges 9 are forced in tightly between the Wires in order to secure them rigidly to the cylinder 1. When this has been done, the liquid under pressure is admitted to the chamber 38 by operating the valve of the exterior conduit which communi- Cates through the thimble 43 with the channel 32. By this means, the cylinder 1 is forced towards the left with respect to the piston 3, since the head of the jack is hard up against the block of concrete through the ring 15. The cylinder 1 draws with it the wires 8 which are thereby tensioned. During the movement of the cylinder 1, the cone which the wires initially formed between the ring 15 and the portion 6 of the cylinder 1 has its apex angle reduced, but the shape and the dimensions of the members of the jack which co-operate with the wires are such that the wires do not come into contact with the bottom of the notches 13 until the cylinder has recoiled to the end of its travel, the conical layer formed by the wires coinciding at that point with the extension of the cone of the anchoring wedge, the pressure of the wires on the internal surface 16 of the ring 15 being eliminated. The elastic extension of the wires during the tensioning operation thus has no friction to overcome against the head of the jack during the tightening period, except that of the rubbing against the lateral walls of the notches 13 which is negligible, and in any case the said notches can be made fairly wide. The only friction is that which exists between the wires and the internal surface 16 of the ring 15, but this friction diminishes as the tension on the wires increases which thus reduces losses due to friction as compared with all known types of jack in which the friction obtaining at the start against the external surface of the head of the jack increases as the tension on the wires increases.

When the wires have been placed under the desired tension, the supply of fluid pressure to the chamber 38 is cut ot and the valve of the conduit which terminates in the thimble 43 is then isolated in order to maintain constant the pressure obtaining inside the chamber 38 and therefore the tension applied to the wires.

The second phase of the operation has the object ot' driving-in the Wedge which secures the wires by means of the rod 22, 23 of the piston 21 whilst the wires are underv tension, in order to x them in the block of concrete whilst they are still under tension. In order to do this, the conduit which ends in the thimble 42 is c ounected to the pump and the chamber 34 is thereby put under pressure, causing the piston 21 to be displaced. One or more holes b formed in the ring 15 enable the movement of the extremity 23 of the piston 21 and thereby the driving of the wedge c to be controlled. The pressure in the chamber 34 is transmitted through the channel 35 to the annular chamber 36 and this creates a slight over-pressure in the chamber 38. This overpressure is not troublesome because of the small annular cross-section of the chamber 36,. When the piston 21 has carried out its function, the chamber 38 is` placed to exhaust by connecting the conduit which ends in the thimble 43 to the reservoir of liquid, Whilst the chambers 34 and 36 are still held under pressure. The force exerted on the piston 3 by the pressure obtaining in the chamber 36 then becomes predominant and the piston and sleeve assembly 3-4-11 moves towards the left of Figure 1, along the piston and rod assembly 21-22-23, against the action of the spring 24. Pressure liquid is continuously supplied to the chambers 34, 36 in order to maintain the pressure obtained therein at a constant level until the ends of the Wedges 9 come in contact with the abutments 14 which causes the said wedges to be loosened and enables them to be removed, thereby freeing the extremities of the wires 8 so that they can be taken out of the jack. The contact between the wedges 9 and the abutments 14 is permitted by the fact that the spring 17 is compressed at the end of the stroke of the piston 3 towards the left.

It should be noted .that at the moment when the chamber 38 is connected to exhaust, whilst the pressure is maintained in the chamber 36, this pressure tends to displace the cylinder 1 towards the right. However this tendency is counteracted by the stiffness or" the reinforcement wires 8.

When the chambers 34 and 36 are finally connected to the exhaust, the spring 17 returns the cylinder 1 with respect to the piston 3, to the position shown in Fig. 1.

The jack which is thus ready for another operation can then be taken away since it is no longer attached to the wires and the ring 15 which remains threaded on the wires is entirely separate from the jack, being simply supported on the front of the latter on a suitable surface 15a. ln order that the ring may be easily removed in spite of the comparative rigidity of the wires 8, it is convenient to form the bell-,mouthed portion 1,6 starting from a relatively large internal diameter of the ring. It will be seen from the drawing that the internal diameter from `which this Haring commences, is appreciably larger than the diameter of the layer of wires at the point of which the layer passes through the external face of the block of concrete b.

The alternative embodiment of Fig. 3 only dilers from the form of embodiment previously described in the manner by which the chambers 34, 36 and 38 are supplied at the various stages of operation of the. jack. The channel 35 of the method of the preceding embodiment between the chambers 34, 36, is replaced by the channel 35a which, instead of being freely open, is controlled by a cylindrical valve 50. The large-diameter left-hand vface 51 of this valve communicates with the chamber 38 through the hollow plug 52 whilst the rod 53 of the said valve, which is of smaller diameter, is subjected to the pressure obtaining in the ,chamber 34. AV second valve 54 controls a further communication between the chambers 34 and 36 which is made through the channels 55 and 56. The left-hand face 57 of this piston Valve 54, provided with the abutment 58 which co-operates with the solid plug 59, receives through the channel 55 the iluid under pressure from the chamber 36. The right-hand face 60 of the said piston valve receives the fluid under pressure from the chamber 34 through the hole 61. The piston valve 54 is loaded, in addition, by a spring 62 which tends 6 to bring it into the position shown in the drawing, in which it closes the ychannel 56 and thus interrupts the connection between the chambers 34 and 36.

The operation is as follows:

When the liquid under pressure is led through the channel 32 into the chamber 38 in order to carry out the tensioning of the wires, as shown in connection with Fig. 1, the pressure which is transmitted to the left-hand face 51 of the piston valve 50 displaces the latter to the position shown in which it closes the channel 35a and cuts oil, in consequence, the communication between the chambers 34 and 36. As the chamber 36 diminishes in volume, the liquid which it contains is placed under pressure and acts on the left-hand face 57 of the piston valve 54 through the channel 55. The piston valve is thus displaced towards the right and opens the channel 56 permitting the liquid from the chamber 36 to pass into the chamber 34 which is placed to exhaust at this stage of the operation. The pressure in the chamber 34 remains less than the force of the restoring spring 24 of the small piston 21 and this latter remains stationary in the position shown in the drawing until the tensioning phase is completed. At this moment, the pressure is maintained in the chamber 38 in such a way as to maintain the wires taut. The cylinder 1 does not move any further with respect to its piston 3, and the pressure in the chamber 36 falls to zero, as does also that in the chamber 34. The spring 62 then returns the piston valve 54 to the position shown in the drawing, thus shutting off the channel 56 and thereby isolating the chamber 36 from the chamber 34. When the chamber 34 is then supplied with liquid under pressure through the channel 31 in order to cause the piston 21 to move towards the right and drive in the wedge, the piston valve 50 is maintained in the position shown in the drawing since the shaft 53 of this valve has a diameter sufliciently small with respect to that of the left-hand .face 51 of the said valve and thus the force exerted on this valve by the pressure from the chamber 38 remains predominant, at least for the normal value of the pressure in the chamber 34 which enables the wedge to be driven in by the piston 21. When the wedge has been driven in, the chamber 38 is placed to exhaust thus releasing the stress of the parts of the wires 8 protruding from the wedge, whilst the pressure in the chamber 34 is maintained by continuously feeding it with pressure liquid. The piston valve 50 then moves towards the left and opens the channel 35a thus putting the chambers 34 and 36 into communication with each other. The pressure which then obtains in the chamber 36 moves the piston 3 of the jack towards the left, the cylinder 1 being held by the stitr'ness of the wires. The pressure in the chambers 34 and 36 is maintained long enough in order that a suicient stroke of the piston 3 towards the left can be obtained for the wedges 9 to be loosened by coming up against the projections 14, in order to free the wires. After the ejection of the wedges, the chamber 34 is placed to exhaust and afterwards also the chamber 36, through the channels 55 and 56 which are at that moment opened by the piston valve 54 which is displaced towards the right against the pull of its spring 62. The operations are now completed.

It will be noted that in the form of embodiment described, the spring 17 of Fig. 1 which serves to bring back by a slight amount the cylinder 1 after the removal of the wedges, is replaced by an assembly of springs 65 which act on the ngers 66, mounted slidably in the conical portion 6 of the cylinder 1, opposite each slot 7 which is vintended to receive a wedge 9. It is by the recoiling motion of these ngers coming up against the projectingr parts 14 with a corresponding compression of the spring 65, that the wedges 9 are loosened. When the chambers .34 yand 36 are put to exhaust, the springs 65 force the cylinder 1 to move towards the left in order that it can take up the position shown in the drawing, in which the members are ready for a fresh operation.

In the two forms of embodiment described above, the

arrangement of the supply channels 31 and 32 on the eudplug 2 of the main cylinder 1 allows the junction members (the thimbles 42, 43) of the external, fluid supply conduits to be placed at a point on the jack at which these conduits and these thimbles run the least risk of being damaged by the manipulations of the jack, whilst in the case of the jacks known up to the present time, the pressure supply points were brought in laterally at points which were quite different, and which hampered the manipulation and involved risk of breakage of the connecting members. An arrangement of the present kind in the improved jack is accompanied by the arrangement of the hollow rod 27 which enables the chamber 34 and thereafter the annular chamber 36 to be supplied through the main piston 3 which is mounted so as to slide inside the said rod.

It will also be noted that the arrangement of the thimbles 42, 43 with their circular seatings 46, 47 permits a variable angular locking of these thimbles about the axis of the said seatings, so that the supply conduits which end in these thimbles, may have any orientation whatever within a sector of 180.

Furthermore, it will be evident that modifications may be made to the forms of embodiment which have been described above, in particular by the substitution of equivalent technical means, without thereby departing from the spirit or from the scope of the present invention.

What I claim is:

1. A hydraulic jack designed for tensioning reinforce? ment wires extending within a concrete structure and protruding therefrom through an opening of an outwardly diverging passage and for anchoring said wires in said passage by means of a tapering wedge shaped to tit said passage, said jack comprising a generally annular member designed to be positioned about said opening and abutted against said structure, said member having a divergent inner surface, the divergence of said surface being substantially greater than that of said passage whereby said wires may be displayed alongpthe peripheral surface of said passage and the inner surface of said member with an increasing divergence, a tubular casing having a closed end and an open end, a tubular piston assembly slidably and liquid-tightly fitted in said tubular casing and having a closed end opposite the closed end of said casing and an open end protruding from the open end of said casing, said open end of said assembly being adapted to accommodate a portion of said protruding wires and to fit against said annular member, a ram slidably and liquid-tightly fitted in said tubular piston assembly and having an operative end adapted to protrude from the open end of said assembly and engage said annular member, said ram being designed for driving said wedge into said passage, wire gripping means on said casing, controllable means for supplying and exhausting pressure liquid to and from the inside space of said tubular casing bounded by said closed ends, and further controllable means for supplying and exhausting pressure liquid to and from the inside space of said tubular piston assembly bounded by the closed end thereof and said ram.

2. l ack as claimed in claim l, wherein the tubular piston assembly comprises, on the outer surface of its protruding portion, longitudinally extending grooves designed for accommodating the protruding portions of the wires, the transverse size of said grooves being substantially larger than the transverse size of said wires, whereby frictional engagement between said wires and said assembly is substantially avoided.

3. Jack as claimed in claim 2, wherein the grooves have slanting bottoms which diverge from the open end of the assembly, the divergence of said bottoms being substantially smaller than that of the inner surface of the annular member.

4. Jack as claimed in claim 3, wherein the divergence of the bottoms of the grooves is substantially equal to that of the passage in the concrete structure.

5. Jack as claimed in claim l, wherein the wire gripping means are so positioned on the casing that, in the absence of pressure liquid in the former-mentioned space, the divergence of the portions of the wires protruding from the annular member is substantially equal to that of the inner surface thereof.

6. Jack as claimed in claim 5, wherein the stroke of the casing relatively to the piston assembly fitting against the annular member, is so adjusted that, at the end of said stroke when pressure liquid is supplied to the formermentioned space, the divergence of the portions of the wires protruding from the annular member is substantially equal to that of the passage in the concrete structure.

7. Jack as claimed in claim l, wherein a part of the outer surface of the tubular piston assembly the closed end thereof is spaced from an opposite part of the inner surface of the tubular casing, said parts bounding an annular liquid-tight space around said assembly.

8. lack as claimed in claim 7, comprising duct means in the piston assembly between the annular space around and the space inside said assembly.

9. Jack as claimed in claim 8, comprising valve means in the duct means.

10. Jack as claimed in claim 9, wherein the valve means is responsive to the differential pressure of the space inside the casing and the space inside the assembly, said valve means being urged towards closing position by an increased pressure in the former-mentioned space and towards opening position by an increased pressure in the latter-mentioned space.

l1. Jack as claimed in claim 10, wherein the valve means is so biased that it only moves to opening position upon a substantial overpressure in the latter-mentioned space.

12. I ack as claimed in claim 9, wherein the valve means is responsive to the pressure obtaining inthe annular space and is urged towards opening position by said pressure, saidl jack further comprising resilient return means for urging said valve means towards closing position.

13. Jack as claimed in claim 1, wherein the wire gripping means comprise longitudinally extending grooves on the outer surface of the tubular casing in the vicinity of the open end thereof, said grooves having opposite side walls adapted to accommodate the wires, and wedgeshaped members adapted to engage said grooves and clamp said wires against said walls when driven along said grooves in the direction of the annular member.

14. Jack as claimed in claim 13, further comprising laterally and outwardly protruding portions integral with the piston assembly and generally registering with the wedge-shaped members in the grooves, said portions being so positioned as to drive said members out of said grooves at the end of the stroke of said piston assembly relatively to the casing upon exhaust of the space inside said casing and supply of pressure liquid to the space inside said assembly.

15. Jack as claimed in claim 14, further comprising spring means arranged for being stressed at the end of the relative stroke of the piston assembly as the wedgeshaped members are driven out of the grooves and for urging said piston assembly away from the closed end of said casing upon exhaust of the pressure in the space inside said assembly.

References Cited inthe tile of this patent UNITED STATES PATENTS 2,371,882 Freyssinet Mar. 20, 1945 FOREIGN PATENTS 543,249 Great Britain Feb. 16, 1942 

